- This is a renewal request for 5 years of support to study CPPD crystal deposition disease. This is a common form of arthritis, particularly in the elderly. Prevalence approaches 50% in those over 80. This disease is associated with acute attacks of gout-like arthritis termed pseudogout, but more importantly, with debilitating degenerative arthritis. These studies are aimed at determining the mechanism(s) of CPPD crystal formation in cartilage so that logical therapeutic and prophylactic interventions may be formulated. This proposal focuses on the role of inorganic pyrophosphate (PPi), the anionic constituent of CPPD crystals, in disease pathogenesis. Disordered PPi metabolism has been strongly implicated in CPPD crystal deposition. Specifically emphasized will be experiments to determine the mechanism controlling PPi generation in the extracellular cartilage matrix (where crystals form) by the ectoenzyme nucleoside triphosphate pyrophosphohydrolase (NTPPPH), which generates extracellular PPi from nucleoside triphosphate substrates such as ATP. Elevated NTPPPH activity has been clinically linked to CPPD deposition disease in studies of joint fluid and diseased cartilage. And NTPPPH is remarkably enriched in articular cartilage vesicles (ACV), matrix vesicles which mineralize to form CPPD in the presence of ATP substrate. They will test the hypotheses that: chondrocytes are the source of extracellular ATP substrate for NTPPPH; that ACV enriched in NTPPPH are biologically regulated; that ACV formation of CPPD crystals is pharmacologically inhibitable; that ACV formation of CPPD crystals is modified by cartilage matrix components; and that a specific molecular form of NTPPPH is necessary for CPPD formation in cartilage and in isolated ACV. New insights into these processes may suggest therapeutic approaches.